The invention relates to power supplies and, more particularly, to DC to DC power supplies in which the output voltage is regulated against variations. Such a power supply is often used to provide a high voltage direct current output when only a low voltage direct current source is available.
A typical DC to DC power supply of the prior art comprises an inverter circuit for changing low voltage direct current to alternating current, a transformer having its primary winding connected to the output of the inverter, and a rectifier circuit connecting the load to the secondary winding of the transformer. The inverter circuit of the power supply usually utilizes switching transistors to alternate the direction of the current through the primary winding, and a regulating circuit which senses the output voltage at the load is normally utilized to control the switching of the inverter transistors. The inverter circuit typically includes a separate pre-regulator circuit utilizing an inductor connected between the DC source and the parallel arrangement of a switching transistor and an input capacitor, with the capacitor furnishing input power to the inverter. The switching transistor is enabled to allow current through the inductor to increase for charging the input capacitor. The on-time of the switching transistor in the pre-regulator is controlled by the regulating circuit in response to the output voltage so that the output voltage is held constant.
Such power supplies have a number of disadvantages. The use of a switching transistor with the inductor generates substantial electromagnetic interference. It is also necessary that the transistors of the inverter circuit which switch the current in alternate directions through the primary winding have no conduction overlap because such an overlap will provide a short-circuit of the input capacitor through the switching transistors, resulting in exceedingly high peak currents which will probably damage those transistors. Thus, a period of dead time is left between current in alternate directions. This dead time causes a loss of power between the input and the output and enlarges the output voltage ripple. If the dead time of the switching transistors in the inverter can be reduced or eliminated, these disadvantages will be substantially reduced.
It is an object of the present invention to provide a new and improved DC to DC power supply.
It is another object of the present invention to provide a DC to DC power supply having increased power handling capabilities.
It is still another object of the present invention to provide a simpler, more compact DC to DC power supply having better operating characteristics than prior art power supplies.